Question: Daniel is 3 times as old as Tiffany and is also 4 years older than Tiffany. How old is Daniel?
Explanation: We can use the given information to write down two equations that describe the ages of Daniel and Tiffany. Let Daniel's current age be $d$ and Tiffany's current age be $t$ $d = 3t$ $d = t + 4$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $d$ is to solve the second equation for $t$ and substitute that value into the first equation. Solving our second equation for $t$ , we get: $t = d - 4$ . Substituting this into our first equation, we get the equation: $d = 3$ $(d - 4)$ which combines the information about $d$ from both of our original equations. Simplifying the right side of this equation, we get: $d = 3d - 12$ Solving for $d$ , we get: $2 d = 12$ $d = 6$.